The present technology relates to a development device which, in image forming processing using a two-component developer, converts an latent electrostatic image into a visible image, and to an image forming apparatus which incorporates such a development device.
In the process of image forming by a method of electronic photography, a member for bearing a latent image, which has been electrified to a uniform electrical potential, is exposed to light corresponding to image information, and thereby an latent electrostatic image is formed upon this latent electrostatic image bearing member, and then this latent electrostatic image is developed into a visible image with a development device. As methods for developing such a latent electrostatic image, there are a single-component development method which uses a magnetic single-component developer or a non-magnetic single component developer, and a two-component development method which uses a two-component developer including a toner and a carrier. The carrier consists of magnetic particles.
With such a two-component method, the carrier and the toner are mixed and ground together and are mutually frictionally electrified, and thereby the toner is carried upon the surface of the carrier. The carrier which is carrying the toner is formed into the shape of projections—so called spikes—upon the surface of a developer bearing member which incorporates a magnet. As for example described in JP 3,305,138 B, the latent electrostatic image is developed due to the toner in the spikes upon the developer bearing member shifting to the latent electrostatic image upon the latent electrostatic image bearing member.
With this two-component development method the device is slightly more complicated as compared to the single-component development method, but this method is very often used, since it is comparatively simple and easy to set the electrical potential of the toner, and since the high speed capability and stability are excellent.
As a method for regulating the layer thickness of the two-component developer upon the surface of the member which bears this developer, apart from a method using a non-magnetic blade, there is also a known method using a magnetic blade (a magnetic member).
However, with such a method which uses a magnetic blade, coarseness can easily occur in half-tone regions in which the reflection density of the image for development is less than 0.3, and in particular in low density regions such as photographic images and the like.
Moreover, if the magnetic blade is thick in the direction along the direction of conveyance of the (two-component) developer (for example if its thickness is 1.0 mm), then the spikes into which the developer has stood up on the developer bearing member become thick and also short, and the shifting of the developer from within these spikes to the latent electrostatic image bearing member is hindered, so that density blotching and whiteout can easily occur in the image when printing the high density regions. Furthermore, the ends of the spikes into which the developer has stood up may become bent over due to the time period required until they leave the magnetic blade becoming long, and in this case the efficiency of development is deteriorated.
An object is to provide a development device, and an image forming apparatus incorporating such a development device, with which the efficiency of development is good, and which can suppress coarseness, light and dark blotching, and whiteout.